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ss7ja [257]
3 years ago
10

Explain why the precise length target DNA sequence doesn't get amplified until the third cycle. You may need to use additional p

aper and a drawing to explain your answer.

Biology
1 answer:
shusha [124]3 years ago
3 0

When you start the PCR amplification reaction, you have a template which has sequences where the primers will anneal. The forward primer anneals in the sense strand and the reverse one in the complementary sequence (see attached figure).

After the first PCR cycle, two types of fragments are obtained. First those which come from tha 5'-3' sequence, that are 3'-5' and will anneal the reverse primer in the following cycle. This fragments have the correct 3' end, but the 5' includes part of the template that doesn't correspond to our target (see attached figure)

Second, those fragments that come from the 3'-5' sequence, that are 5'-3' and will anneal the forward primer. This fragments also have the correct 3' end, but the 5' includes part of the template that doesn't correspond to our target (see attached figure).

Now, during the second cycle, are produced the first fragments that have the precise length of the sequence that we want to amplify (see attached figure).

So, it's not until the third cycle that the reaction starts amplifying exactly the sequence of desired length.

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Answer:

Hypertonic

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3 years ago
4. A polypeptide has the following amino acid sequence: Met-Ser-Pro-Arg-Leu-Glu-Gly In the mutant below, indicate the type of mu
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4)

A single base pair at the first position of the Arg codon i.e. CGA has been deleted. Due to the deletion, the reading frame has shifted one nucleotide backwards, altering the amino acid sequence of the protein.

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The genomic DNA sequence is 5'-ATG ATA CTA AGG CCC-3'. Therefore, the complementary mRNA will be 5'-UAC UAU GAU UCC GGG-3'. According to the genetic code, this mRNA sequence encodes the following amino acid sequence: Tyr Tyr Asp Ser Gly

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5'-ACUGUAAUGGAGUCAGAUGAUGCAUUAAGGAGAAAUUGAAAUAAA-3'

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This is a single base pair insertion and frameshift mutation that shifts the reading frame one base pair forwards. The codon that was originally GAG coding for glutamic acid (Glu) gets converted to GGA that codes for glycine. Therefore, the amino acid sequence has been altered but the polypeptide chain will still have 13 amino acids.

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